1. Field
One or more embodiments described herein relate to a phase-locked loop circuit.
2. Discussion of the Related Art
It is difficult to secure voltage head room in designing an analog circuit with a deep sub-micron manufacturing process. This is because a deep sub-micron manufacturing process provides low supply voltage and relatively high threshold voltage. Analog circuits have been used in a variety of applications.
An analog circuit in a phase-locked loop circuit has been developed using a thick oxide transistor, which operates based on higher supply voltage. In contrast, a digital circuit in a phase-locked loop circuit may be implemented using a thin oxide transistor in a reduced area.
When an analog circuit is used in the phase-locked loop circuit, the analog circuit may include a voltage controlled oscillator (VCO) delay cell. The VCO delay cell may be implemented by a thin oxide transistor to generate a signal in the GHz frequency range, even though the VCO delay cell is a sort of analog circuit. In operation, the VCO delay cell may be physically destroyed by various factors, including but not limited to a relatively high voltage signal generated by the analog circuit.